NY flood: New records set for rainfall totals, without a hurricane

Peter D. Kramer, Rockland/Westchester Journal News
Updated ·4 min read

While Sunday’s storm didn’t bring hurricane-force winds or even hurricane-level attention in advance, it delivered record-setting hurricane-level rainfall totals in the Hudson Valley.

The unusual thing was that the storm wasn’t tied to a hurricane, said Nick Bassill, who is director of research and development at the University at Albany Center of Excellence, where the New York State Mesonet tracks real-time weather data from 126 field stations.

“This was tied to nothing other than just that it was really, really, really humid out and there was lots of available moisture,” Bassill said. “Conditions just got right to have the storms go over the same spot over and over again.”

Bassill said research teams will want to look at the water temperatures in the hours before the storm, which were “well above average.”

“I presume that that probably contributed at least a little bit to the moisture,” he said. “It's hard to say with any kind of confidence, but these are the types of events we expect to see with more frequency as we continue to move into a warming climate.”

Nick Bassill watches a wall of monitors in the University at Albany’s ETEC research and development complex on July 10, 2023, the day after a slow-moving drencher of a storm set record rainfall totals across the Hudson Valley, washed out roads and killed at least one resident. Bassill is involved with the New York State Mesonet, a network of 126 weather stations that updates weather conditions every five minutes. The Mesonet tracked Sunday's storm as it veered south toward Orange County, giving emergency teams vital data in real-time.

Rain, and records, fall

Sunday's storm was one for the books. Along with a whole lot of rain, rainfall records fell — some dating to 2021’s Hurricane Ida — in Somers, Beacon and Dover Plains.

In Somers, the record for rainfall over 24 hours was 5.30 inches. Sunday's storm brought 5.96 inches.  The record for rainfall in one hour was 1.59 inches. Sunday's storm brought 2.17 inches.

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Beacon broke its three-hour rainfall record, set during Ida. Its old record was 2.37 inches over the course of three hours. Sunday’s storm brought 3.13 inches in one three-hour period.

Dover Plains’s 24-hour rainfall record of 5.02 inches, set in Ida, is now 5.39 inches after Sunday’s storm.

This map shows the precipitation recorded over the 24-hour period ending July 10, 2023 at 9 a.m. at the 126 weather stations comprising the New York State Mesonet. While the Hudson Valley saw totals of 4.8 inches in Beacon and 6 inches in Somers, but citizen readings and other data suggests totals as high as 10 inches.
This map shows the precipitation recorded over the 24-hour period ending July 10, 2023 at 9 a.m. at the 126 weather stations comprising the New York State Mesonet. While the Hudson Valley saw totals of 4.8 inches in Beacon and 6 inches in Somers, but citizen readings and other data suggests totals as high as 10 inches.

Changing path

The storm was originally expected north, in Albany. But Bassill, who lives in Albany, could watch it veer south and take deadly aim on Orange County in real-time, thanks to the New York State Mesonet, which gathers and reports data in real-time, updating every five minutes, not the on-the-hour updates the National Weather Service station gives.

“When people went to bed on Saturday night, the expectation was that the heaviest rain for the storm was going to be from the Catskills through Albany, about four or five inches of rain,” he said. “Spots like West Point and Orange County were only forecast to get an inch or two of rain, which would be a lot, but certainly not flooding level.

“But as the event started unfolding, it became very clear that we were seeing much higher rainfall totals further to the south. And not very high rainfall totals in places like where I live. It’s important to have that network of observations to tell you your expectations are not being met or they're being exceeded here.”

This map shows the maximum one-hour precipitation over the period ending July 10, 2023 at 9 a.m. at the 126 weather stations comprising the New York State Mesonet. The station at Somers recorded 2.2 inches of rain in single hour on July 9, 2023, breaking a record set in 2021's Hurricane Ida.
This map shows the maximum one-hour precipitation over the period ending July 10, 2023 at 9 a.m. at the 126 weather stations comprising the New York State Mesonet. The station at Somers recorded 2.2 inches of rain in single hour on July 9, 2023, breaking a record set in 2021's Hurricane Ida.

West Point targeted

The Mesonet has stations across the Lower Hudson Valley, Bassill said, creating a sort of ring around West Point and Highland Falls, the areas hardest hit by Sunday's storm.

"Their peak rainfall was about six inches Sunday afternoon, overnight," he said. But there are other measures, less official, that saw higher totals.

"There are other citizen measurements that are closer to West Point and I think there was 8.12 inches reported there. And the radar estimates how much rain fell as well. It's not really perfect. It can't really be used as an observation because it's just an estimate, not ground truth. But that suggests that as much as 10 inches fell in a small area near the West Point, Highland Falls area."

The National Weather Service's unofficial citizens network recorded 8.12 inches of rain at the United States Military Academy at West Point on July 9, 2023.
The National Weather Service's unofficial citizens network recorded 8.12 inches of rain at the United States Military Academy at West Point on July 9, 2023.

Real-time warnings

The Mesonet isn't a forecasting tool. It shows weather-watchers what's happening, not what's going to happen next week or next month.

But it does tell forecasters if their expectations are holding true. They can alert first-responders if conditions change.

The weather network came about just after 2011’s Hurricane Irene and has helped to warn the state’s emergency management system to storms' changes, in real-time.

The Mesonet also partners with ConEd in New York City, alerting the power company when certain areas receive more than three-quarters of an inch of rain.

Reach Peter D. Kramer at pkramer@gannett.com.

This article originally appeared on Rockland/Westchester Journal News: Hudson Valley flood: Rain records set without a hurricane